<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>实例1</title>
    <style>
        div{
            width: 500px;
            height: 100px;
            margin: 0 auto;
        }
        .a,.b,.c{
            width: 100px;
            height: 100px;
            background-color: skyblue;
            float: left;
            margin-left: 40px;
        }
        .c{
            float: right;
        }
    </style>
</head>
<body>
    <div>
        <div class="a"></div>
        <div class="b"></div>
        <div class="c"></div>
    </div>
</body>
</html>